This invention provides a process for reducing the amount of haloorganic compounds in water. The invention may be usefully applied to any catchment of water and is particularly useful for the recovery of potable water from groundwater which has become contaminated by pesticidal haloorganic compounds. Such contamination may occur, for example, from agricultural run-off, or from accidental discharge of such compounds into the water-collecting system of an aquifer.
The contamination of underground water with agricultural chemicals was once considered unlikely, but there is mounting evidence that it is now occurring in wide areas of America. It was formerly thought that pesticidal residues would adhere to soil particles, and disappear naturally before they could significantly contaminate the groundwater. However, it has been found that for many agricultural chemicals instead of clinging to the soil at the surface, they percolate rapidly into underground water-bearing formations. No one knows what effect, if any, the generally low levels of, e.g., pesticides may have on human and farm animal health, but there is concern among environmentalists that there is insufficient experience to be assured that no problem exists.
Among the 500 or so known pesticides, about 90 are haloorganic compounds having wide utility, i.e. for controlling household and agricultural pests. Halogenated aliphatic compounds such as mixtures containing 1,3 dichloropropene, 1,2 dichloropropane, and/or dibromochloropropane have proven effective as soil fumigants to control, e.g. nematodes; halocyclodiene compounds marketed under tradenames such as Chlordane, Dieldrin, and Aldrin have been used to control e.g., cockroaches, ants, termites and other household pests, soil insects and many pests of vegetable and field crops; however such usage is now severely regulated.
Some widely used halogenated organic solvents such as trichloroethylene and carbon tetrachloride are also identified as organic contaminants in ground waters where leaks or spills from industrial sources have occurred.
Generally, pesticidal haloorganic compounds are only poorly soluble in water and are resistant to natural degradation in groundwater. Accordingly contamination of groundwater, although typically in very low concentration of a few parts per million, depending upon the particular haloorganic compound and on local conditions may persist for months, and possibly years. A method to expedite biotreatment of halogenated hydrocarbons is disclosed in U.S. Pat. No. 4,401,569, however, this is still time consuming and may not be suitable where the contaminated water is needed for immediate use.
It is known from U.S. Pat. No. 4,401,570 to remove organic contaminants from alkaline wastewater by a combination of acidification and extraction with a C.sub.5 -C.sub.10 hydrocarbon, however, the addition of chemicals for acidification and neutralization may be undesirable, particularly where potable water is required.
It has been proposed to extract chlorinated hydrocarbons from water into hydrocarbon solvents such as undecane and kerosene, however, the relatively high solubility of such solvents in water results that the residual solvent remaining in the water after extraction would be at undesirably high levels where potable water is needed. Further the typically substantial aromatic content of most kerosene would be objectionable under the regulations of many state jurisdictions. In addition to having a favorable equilibrium distribution coefficient for the pesticidal haloorganic compounds, a solvent is needed which would have excellent transparency and stability under the conditions of regeneration to enable reuse of the solvent, and permit continuous operation. Such a solvent, process and apparatus to carry it out have now been found.